Centralizers may be coupled with oilfield tubulars (e.g., casing, drill pipe, etc.), so as to maintain a generally annular standoff between the oilfield tubular and a surrounding tubular (e.g., casing, liner, or the wellbore wall itself) in which the oilfield tubular is disposed. The centralizers may be coupled with the tubulars, e.g., disposed on, and generally maintained at an axial position, or a range of axial positions, with respect to the tubular. Among other applications, centralizers are commonly employed to facilitate filling the annulus between the oilfield tubular and the surrounding tubular with cement.
One type of centralizer is a bow-spring centralizer. Bow-spring centralizers generally have two annular end collars and multiple, flexible, bow-shaped members extending therebetween. The bow-shaped, centralizing members may elastically flex in a radial direction, so as to engage the wellbore wall. Other types of centralizers include rigid and semi-rigid centralizers, which may have less-flexible, or rigid, centralizing members, as compared to the bow-spring centralizer.
Some wells present restrictions that reduce the diameter differential between the surrounding tubular and the oilfield tubular (i.e., the “tolerance”). Such restrictions may be caused, for example, by an inner-diameter restriction, a dogleg, a turn, sloughing, etc. The tolerance provided by some restrictions may be relatively small. Accordingly, when encountering these close-tolerance restrictions, bow-spring centralizers may be forced to contract the centralizing members thereof radially against the tubular, so that the centralizer may pass through the restriction while at least substantially maintaining structural integrity.
Once past the restriction (e.g., as the tubular is moved in the wellbore), and thus exiting the close-tolerance section, the collapsed centralizing members may elastically return generally to their pre-collapsed (i.e., expanded) state. A failure to elastically return to their pre-collapsed state may cause the centralizing members to not properly centralize the tubular, potentially allowing the tubular to contact the wellbore wall or otherwise form a non-uniform standoff. When used in advance of wellbore cementing, such a non-uniform standoff may reduce a wall thickness of the cement around a portion of the tubular.